Systems and methods for printing sensor circuits on a sensor mat for a steering wheel

ABSTRACT

Systems and methods of printing sensor loops on a sensor mat for use in a steering wheel are disclosed herein. For example, the sensor mat may include a base substrate, one or more printed sensing loops, and an insulating material. The printed sensing loops are made with conductive ink that is disposed upon the base substrate or the insulating layer from a print head and adheres thereto. These sensor mats are versatile with respect to the type of base substrate and insulating materials that may be used, the shape of the sensing loops, and the area each loop may occupy. Shielding loop(s) may also be printed adjacent the sensing loop(s). This configuration allows shielding for the sensing loops as part of the sensing mat, which may reduce the thickness of the steering wheel rim and manufacturing and installation times.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patent application Ser. No. 14/728,366 filed on Jun. 2, 2015, now U.S. Pat. No. 10,114,513, which, in turn, claims priority to U.S. Provisional Patent Application No. 62/006,312, entitled “Systems and Methods for Printing Sensor Circuits on a Sensor Mat for a Steering Wheel,” filed Jun. 2, 2014, the contents of both earlier applications noted above incorporated by reference in their entireties as if set forth fully herein.

BACKGROUND

Current steering wheel designs may include one or more sensor mats around a rim of the steering wheel frame that are configured for detecting the presence of a driver's hand using capacitive-type sensing. Known sensor mats include a wire loop that is sewn to a fabric or foam substrate.

The steering wheel frame is typically made of metal, such as a magnesium alloy or steel and can be a source of interference for the signal(s) in the sensing mat.

Thus, existing sensor mats may be time consuming to manufacture, which includes designing a wire stitch layout for the sensor and designing the wire stitch layout for the shield, each being on separate mats that must fit correctly over the complex curve shape of the steering wheel rim. In addition, the pattern may need to be redesigned depending on which areas should provide sensing and the vehicle manufacturer's steering wheel specifications, which can be time consuming. Furthermore, the manufacturing process and available materials limits the ability to use the available space on the base substrate.

Accordingly, there is a need in the art for an improved sensor mat and method for making the same.

BRIEF SUMMARY

Systems and methods of printing sensor loops, or circuits, on a sensor mat for use in a steering wheel are disclosed herein. In particular, a sensor mat according to various implementations includes a base substrate, one or more printed sensing loops, and a dielectric or insulating material. The printed sensing loops are made with conductive ink that is disposed upon the base substrate or the insulating layer from a print head, for example, and adheres thereto. These sensor mats are versatile with respect to the type of base substrate and insulating material used and the shape of the sensing loops and the area each loop occupies. In addition, in certain implementations, the sensor mats include one or more printed shielding loops adjacent the sensing loops and separated from the sensing loops by a layer of insulating material. The thickness of the insulating material, which separates the sensor from the shield, can be specified based on the sensor/shield layout configuration. Increasing the thickness can help reduce noise effects between the sensor and shield and also prevent ‘effective shorting’ due to construction variation. This configuration allows shielding for the sensing loops as part of the sensing mat, which may reduce unwanted electrical interference with the electrical signal(s) carried by the sensor mat caused by the sensor mats proximity with the steering wheel rim, the thickness of the steering wheel rim, and manufacturing and installation times.

According to various implementations, the conductive ink may include silver, carbon, carbon nanotube (CNT), graphene, or copper. In addition, the base substrate may include a polymer foam, a polymer film, leather, vinyl, felt, or non-woven material. The insulating materials may include any suitable dielectric or insulating material, such as polyamides, or other printable dielectric inks.

In one implementation, the one or more sensing loops are printed onto the base substrate. The insulating material is a first insulating material, and one or more shielding loops are printed with the conductive ink onto the first insulating material. A second insulating material is disposed over the one or more shielding loops. The one or more sensing loops include a first sensing loop and a second sensing loop, and the one or more shielding loops include a first shielding loop and a second shielding loop. The first shielding loop is disposed adjacent the first sensing loop, and the second shielding loop is disposed adjacent the second sensing loop. However, in an alternative implementation, the first shielding loop may be disposed adjacent the first and second sensing loops.

The sensor mat may further include one or more shielding feed traces printed with conductive ink onto the first insulating material. Each shielding feed trace extends from a corresponding shielding loop toward an edge of the first insulating material. The sensor mat may also include one or more sensor return traces printed with conductive ink onto the base substrate. The sensor return traces extend from a corresponding sensing loop toward an edge of the base substrate.

In an alternative implementation, one or more shielding loops are printed with conductive ink onto a second insulating material disposed over the base substrate. The insulating material disposed over the sensing loops is a first insulating material, and a third insulating material is disposed over the one or more shielding loops. The one or more sensing loops are printed onto the third insulating material.

In addition, according to various implementations, a system for hand sensing on a steering wheel includes a sensor mat, such as the sensor mats described above, and an electronic control unit (ECU) that is in communication with the sensor mat. The ECU includes a processor and a power source. The processor is configured for receiving a signal from at least one of the one or more sensing loops and determining an indication associated with the signal.

In certain implementations in which the sensor mat includes one or more shielding loops and shielding feed traces, the system includes shielding feed wires that extend between the ECU and the respective shielding feed traces. The processor is configured for instructing the power source to selectively generate a voltage signal through the one or more shielding loops via the shielding feed wires and the shielding feed traces. The system may also include sensor return wires that extend between the ECU and the respective sensor return traces. The signal received from at least one of the sensing loops is received by the processor via the sensor return wire and the sensor return trace.

According to other various implementations, a method of manufacturing a sensor mat includes (1) printing one or more sensing loops with conductive ink adjacent a base substrate that is configured for being installed around the steering wheel frame rim and (2) disposing a layer of insulating material over the one or more sensing loops. In one implementation, printing the one or more sensing loops includes printing the one or more sensing loops on the base substrate. In this implementation, the insulating material is a first layer of insulating material, and the method also includes printing one or more shielding loops with conductive ink onto the first insulating layer and disposing a second layer of insulating material over the one or more shielding loops.

In an alternative implementation, the layer of insulating material is a first layer of insulating material, and the method includes printing one or more shielding loops with conductive ink onto a second insulating material disposed on the base substrate and disposing a third layer of insulating material over the one or more shielding loops. The one or more sensing loops are printed onto the third layer of insulating material.

The method may also include selectively generating a voltage signal through one or more of the shielding loops that are disposed adjacent the sensing loops. The voltage signal is sufficient to shield the adjacent sensing loop from electrical interference from a metal steering wheel frame.

BRIEF DESCRIPTION OF THE DRAWINGS

The components in the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding parts throughout the several views.

FIG. 1A illustrates a cross sectional view of layers in a steering wheel.

FIG. 1B illustrates a perspective view of a sensor mat layer with multiple zones and a shielding mat.

FIG. 2 illustrates a sensor mat.

FIG. 3 illustrates a top view of a sensor mat according to one implementation.

FIG. 4 illustrates a cross sectional view of the sensor mat in FIG. 3.

FIG. 5 illustrates a schematic view of a steering wheel system using the sensor mat shown in FIG. 3.

FIG. 6 illustrates a top view of a sensor mat according to another implementation.

FIG. 7 illustrates a cross sectional view of the sensor mat in FIG. 6.

FIG. 8 illustrates a top view of a sensor mat according to another implementation.

FIG. 9 illustrates a cross sectional view of the sensor mat in FIG. 8.

FIG. 10 illustrates a top view of a sensor mat layer according to another implementation.

FIG. 11 illustrates a cross sectional view of the sensor mat in FIG. 10.

FIG. 12 illustrates a top view of a heater mat layer according to one implementation.

DETAILED DESCRIPTION

Systems and methods of printing sensor loops, or circuits, on a sensor mat for use in a steering wheel are disclosed herein. In particular, a sensor mat according to various implementations includes a base substrate, one or more printed sensing loops, and a dielectric or insulating material. The printed sensing loops are made with conductive ink that is disposed upon the base substrate or the insulating layer from a print head, for example, and adheres thereto. These sensor mats are versatile with respect to the type of base substrate and insulating material used and the shape of the sensing loops and the area each loop occupies. In addition, in certain implementations, the sensor mats include one or more printed shielding loops made with conductive ink adjacent the sensing loops and separated from the sensing loops by a layer of insulating material. The thickness of the insulating material, which separates the sensor from the shield, can be specified based on the sensor/shield layout configuration. Increasing the thickness can help reduce noise effects between the sensor and shield and also prevent ‘effective shorting’ due to construction variation. This configuration allows shielding for the sensing loops as part of the sensing mat, which may reduce unwanted electrical interference with the electrical signal(s) carried by the sensor mat caused by the sensor mats proximity with the steering wheel rim, the thickness of the steering wheel rim, and manufacturing and installation times.

To date, printed conductive inks have not been used in steering wheel sensor or heating mats because of the complex three-dimensional geometry of the steering wheel and the possibility of visual read-through on the top surface of the steering wheel. In addition, there is concern about the ink patterns breaking when the mat is stretched and/or wrapped tightly around the steering wheel frame rim and adjacent to spokes in the steering wheel frame. However, applicants have discovered various solutions for avoiding these issues. For example, according to one implementation, conductive inks having suitable elongation and flexibility characteristics may be printed onto a sufficiently stretchable base substrate, which allows the sensor mat to be stretched more evenly around the steering wheel frame rim and avoid undesirable bunching of the base substrate. According to another implementation, a polymeric foam layer may be disposed between the mat and the skin, which prevents read through. This implementation may be particularly useful when the stretchable ink and base substrate cannot be used for the particular steering wheel rim configuration and some bunching of the base substrate is unavoidable. And, according to yet another implementation, the base substrate onto which the conductive ink is printed may be the underside of the leather skin that is installed as the outermost layer of the steering wheel, which alleviates concerns about read through and further reduces the materials used in the manufacturing and installation process and the time and costs associated with installation. These and other implementations are discussed in more detail below in relation to FIGS. 3 through 11.

FIG. 1A illustrates a cross-sectional view of a steering wheel rim sensing system that includes a sensor mat, a shielding mat, and a heater mat. In particular, the rim includes a frame 12, a first over molded layer (e.g., foam) 14, the heater mat 6, the shield mat 7, the sensor mat 8, and an outer skin 20. Some sensor mat designs may include one sensing zone or multiple sensing zones that are spaced apart from each other. FIG. 1B illustrates a perspective view of a sensor mat that has more than one sensing zone and a separate shielding mat having more than one conductive zone that is disposed between the sensor mat and the steering wheel frame. Each conductive zone on the shielding mat shields the portion of the sensor mat that is adjacent to it.

Each wire loop having its own return trace (or return wire connected thereto) defines a discrete sensing circuit, or zone. FIG. 2 illustrates a perspective view of an exemplary sensor mat having this configuration. Sensor return wires that extend from the sensing zones may present an additional source of electrical interference for other sensing zones, particularly when the sensor return wire from one sensing zone is routed close to another sensing zone. To limit interference, attempts are made to route the sensor return wires to avoid the various zones, but this configuration is not always a viable option due to space limitations on the sensor mat and/or the configuration of the steering wheel. Applicants have also discovered systems and methods for selectively shielding one or more sensing loops at a time.

For example, FIG. 3 illustrates a top view of a sensor mat 10 according to various implementations. The sensor mat 10 includes a base substrate 12, one or more sensing loops 14 a, 14 b, 14 c that are printed with conductive ink on the base substrate 12, and a sensor return trace 16 a, 16 b, 16 c printed on the base substrate 12 and extending between each sensing loop 14 a-14 c, respectively, and one end 18 of the base substrate 12. The one or more sensing loops 14 a, 14 b, 14 c are responsive to input in the areas designated generally as “zone 1”, “zone 2”, and “zone 3”, respectively. The area outlined designating each zone may have a suitable circuit pattern within the designated area. For example, the circuit pattern may have a substantially zigzag arrangement, a substantially spiral arrangement, a grid pattern arrangement, a cross-hatch arrangements, or a solid area arrangement.

In addition, in other implementations, there may be one or more zones, and these areas or circuit patterns may be shaped differently or disposed on other portions of the base substrate 12. The number, shape, and relative positions of the zones on the base substrate may be determined based on the sensing needs for the sensor mat 10 and the shape of the steering wheel for the particular vehicle. Furthermore, the conductive ink circuits that make up sensing loops 14 a, 14 b, 14 c may extend over a portion of the general area of the zone but not necessarily cover substantially all of the zone.

As shown in FIG. 3, the sensor return traces 16 a, 16 b, 16 c extend from one side of the sensing loop area 14 a, 14 b, 14 c, respectively, and over a portion of the base substrate 12 that is not part of a sensing zone. Accordingly, the respective return traces 16 a, 16 b, 16 c do not interfere with signals carried by each other. However, this layout may not be suitable for all steering wheel configurations. For example, as discussed below in relation to FIGS. 8 and 9, if more sensing zones are required or if different inputs are to be received from the one or more of the sensing zones, there may not be sufficient space available on the base substrate for printing the sensor return traces such that they do not extend over another sensor return trace or over another sensing loop area.

In addition, as shown in FIG. 4, the sensor mat 10 includes a first dielectric or insulating layer 13 disposed over the sensing loops 14 a-14 c and sensor return traces 16 a-16 c. One or more shielding loops 19 a, 19 b, and 19 c are printed with conductive ink on the layer 13. The shielding loops 19 a-19 c extend over the area defined by the sensing loops 14 a-14 c and the sensor return traces 16 a-16 c, respectively. A shielding feed trace 17 a, 17 b, 17 c extends between each shielding loop 19 a, 19 b, 19 c, respectively, and the end 18 of the base substrate 12. A second dielectric or insulating layer 15 is disposed over the shielding loops 19 a-19 c and the shielding feed traces 17 a-17 c. Similar to the sensor return traces 16 a-16 c, the shielding feed traces 17 a-17 c extend adjacent the shielding loops 19 a-19 c but not over them.

The printing system used may include screen printing, ink jet printing, or pad printing, for example. The conductive ink may include conductive materials such as silver, carbon, CNT, graphene, copper, or other suitable conductive material. For example, according to various implementations, the conductive ink is able to elongate a minimum of about 10% without significant characteristic changes. In certain implementations, silver or carbon based inks (e.g., graphene) may be used because they can withstand at least 10% elongation without breakage or significant characteristic changes, such as changes in resistance. In addition, the conductive ink used for printing the sensing loops may be the same conductive ink used for printing the shielding loops, or different inks may be selected. Furthermore, the conductive material may be modified with additives, such as a polymer such as polyurethane, to affect the resistance.

Dielectric materials used may include polyamide-based material or other suitable insulating materials. In certain implementations, the insulating material may be the base substrate or a dielectric layer printed thereon and/or over printed sensing or shielding loops. In addition, the thickness of the insulating material may vary based on the density of the loop configuration adjacent to the insulating material. For example, the thickness may range from about 0.5 mm to about 1.0 mm or may be greater than or less than this range. Increasing the thickness can help reduce noise effects between the sensor and shield and also prevent ‘effective shorting’ due to construction variation. The base substrate may include felt, leather, a foam or film (e.g., polyurethane, polyethylene, or other suitable polymer), or other suitable non-woven materials capable of receiving and holding the printed conductive ink thereon. In various implementations, the base substrate has the ability to elongate between about 5% to about 20%. Substrates having a lower elongation tend to be more difficult to wrap around a steering wheel. As an example, top grain leather has an elongation characteristic of about 13±5% using a reference force (e.g., about 9 kg), and split grain leather has an elongation characteristic of about 5±3%.

The amount of stretching allowed by the substrate and the ink is taken into consideration when selecting the substrate, conductive ink, and the pattern of the loop(s) to prevent damage to the ink when the substrate is stretched around the steering wheel. In certain implementations, the conductive ink and the base substrate are selected such that the maximum elongation of the base substrate is substantially the same as the minimum elongation of the conductive ink. For example, in one implementation, a relatively stretchable non woven material, such as a non woven material having a maximum elongation of about 10% may be selected for the base substrate 12, and a graphene based ink having a minimum elongation of about 10% may be selected for the conductive ink. Also, depending on the shape to be wrapped around the steering wheel frame rim, the printed pattern may be selected to increase the robustness of the wrapping, elongation, and stretch processes required of the application. As a particular example, cross-hatching or zigzag patterns may be useful for this purpose.

As shown in FIG. 5, the steering wheel system includes an electronic control unit 40 that includes a processor 41 and a power source 42. The ECU 40 is in electronic communication with one or more other vehicle systems (not shown) and the sensor mat 10 via the sensor return traces 16 a-16 c for the sensor loops 14 a-14 c, respectively, and shielding feed traces 17 a-17 c associated with each of the shielding loops 19 a-19 c, respectively.

The processor 41 is configured for detecting input from a driver, such as presence of a hand, adjacent each sensing loop 14 a-14 c. In one implementation, signals from one or more sensing loops 14 a-14 c are communicated to the processor 41 through sensor return traces 16 a-16 c, respectively, and sensor return wires (not shown separately) that extend from each sensor return trace 16 a-16 c to the ECU 40. For example, the signal may be generated through capacitance-type sensing in one or more of the sensing loops 14 a-14 c and received by the processor 41. The processor 41 may compare the signal to a range of signals that indicate various inputs. For example, the signals may be associated with various types of user input, such as a presence of a hand, a touch, a grip, a swipe motion, a tap motion, a double tap, a tap and hold, or a combination thereof from the signal received by the processor 41. The processor 41 may also control the level of current and/or frequency of the voltage signal generated by the power source 42 and when the level of current and/or the frequency of the voltage signal may be increased or decreased.

The power source 42 is configured for generating a voltage signal through the one or more shielding loops 19 a-19 c via one or more shielding feed wires that are connected to each of the one or more shielding feed traces 17 a-17 c, respectively. The voltage signal is configured for shielding the one or more sensor loops 14 a, 14 b, 14 c that are adjacent the shielding loop(s) 19 a, 19 b, 19 c. The shielding voltage signal may be a frequency-specific signal to shield the area adjacent the shielding loops 19 a-19 c. The frequency-specific signal of the shielding loops is configured for matching, as close as possible, the capacitance voltage signal generated for the respective sensing loops 14 a-14 c.

An electric current in the shielding loops may be less than about 200 microamperes. In certain implementations, the current may be between around 9 and around 11 microamperes, and in one implementation, the electrical current may be around 10 microamperes.

When installed in a steering wheel system, the sensor mat 10 is oriented such that the one or more shielding loops 19 a-c are disposed between the steering wheel frame and the one or more sensing loops 14 a-c.

The implementation shown in FIGS. 6 and 7 is similar to the implementation described above in relation to FIGS. 3 and 4 but instead includes a shielding loop 39 printed directly onto a first dielectric or insulating layer 33 a disposed on the base substrate 32 and a sensing loop 34 printed onto a second dielectric or insulating layer 33 b disposed over the shielding loop 39. Alternatively (not shown), the shielding loop 39 may be printed onto the base substrate 32 if the base substrate 32 is a sufficient insulating material. The hatched area depicts the general area from which the sensing loop 34 receives input. The shielding loop 39 is depicted by the dotted area. A third dielectric or insulating layer 33 c is disposed over the sensing loop 34. Similar to the implementation described above in relation to FIGS. 3 and 4, the sensor mat 30 is oriented such that the shielding loop 39 is disposed between the steering wheel frame and the sensing loop 34 when installed in the steering wheel system.

FIGS. 8 and 9 illustrate an implementation of a sensor mat 20 that includes dielectric layers, printed shielding loops, and printed sensing loops disposed in a stacked and vertically off-set arrangement such that shielding loops are provided between each sensor loop or sensor return trace to shield the signals therein. The sensor mat 20 includes a first dielectric layer 23 a disposed directly onto the base substrate 22. A first shielding loop 29 a its shielding feed trace 27 a are printed on the first dielectric layer 23 a. A second dielectric layer 23 b is disposed over the first shielding loop 29 a and trace 27 a. A first sensing loop 24 a and its corresponding sensor return trace 26 a are printed on the second dielectric layer 23 b above the first shielding loop 23 a. A third dielectric layer 23 c is disposed over the first sensing loop 24 a and its sensor return trace 26 a. A second shielding loop 29 b and its corresponding shielding feed trace 27 b are printed on the third dielectric layer 23 c and next to the first shielding loop 29 a when viewed from the top of the mat 20 (see FIG. 8). A fourth dielectric layer 24 d is disposed over the second shielding loop 29 b and its shielding feed trace 27 b. A second sensing loop 24 b and its sensor return trace 26 b are printed on the fourth dielectric layer 24 d above the second shielding loop 29 b. A fifth dielectric layer 24 e is disposed over the second sensing loop 24 b and sensor return trace 26 b. A third shielding loop 29 c and its shielding feed trace 27 c are printed on the fifth dielectric layer 24 e next to the second shielding loop 29 b as viewed from the top of the mat 20. A sixth dielectric layer 24 f is disposed over the third shielding loop 29 c and its shielding feed trace 27 c. A third sensing loop 24 c and its sensor return feed 26 c are printed on the sixth dielectric layer 24 f above the shielding loop 29 c, and seventh dielectric layer 24 g is disposed over the third sensing loop 24 c and its sensor return trace 26 c.

Having multiple, separate circuits of shielding loops 29 a-29 c allows the shielding loops 29 a-29 c to selectively shield one or more sensing zones. The shielding loops 29 a-c receive voltage signals that prevent the steering wheel frame from interfering with the signals in the respective sensing loops 24 a, 24 b, 24 c and the sensor return traces 26 a, 26 b, 26 c. In other implementations (not shown), there may be other combinations of shielding loops and sensing loops.

FIGS. 10 and 11 illustrate an alternative implementation that includes sensor return wires 56 a-56 c that are connected to the sensing loops 54 a-54 c, respectively, and extend upwardly through insulating material 53 a disposed over the sensing loops 54 a-54 c. In particular, the sensor mat 50 includes shielding loops 59 a-59 c and shielding feed traces 57 a-57 c extending from the respective loops 59 a-59 c that are printed on the base substrate 22. In this implementation, the base substrate 22 acts as an insulating layer. A first dielectric or insulating layer 55 is disposed on the shielding loops 59 a-59 c and traces 57 a-57 c. Sensing loops 54 a-54 c are printed on the first insulating layer 55. Sensor return wires 56 a, 56 b, 56 c are connected to sensing loops 54 a, 54 b, 54 c, respectively, directly or via sensor return traces (not shown). A second dielectric or insulating layer 53 a is disposed over the sensing loops 54 a-54 c, and the sensor return wires 56 a-56 c extend through and are laid above the second insulating layer 53 a. A third dielectric or insulating layer 53 b is disposed over the sensor return wires 56 a-56 c.

In alternative implementations (not shown), sensor return wires may be connected to printed sensor loops directly. In addition, the sensor return wires may be disposed in different dielectric or insulating layers from other sensor return wires. Furthermore, shield feed wires may be connected to the printed shielding feed traces or connected directly to the shielding loops. The shield feed wires may also be disposed in one or more dielectric or insulating layers that are separate from the shielding loops and other shield feed wires.

Sensor mats having sensor loops defined by an area of printed conductive ink and, optionally, shielding loops defined by an area of printed conductive ink, allow manufacturers more flexibility with the type of substrates that may be used, may reduce the thickness of the steering wheel rim, may be less time consuming to manufacture and install, and allow for some level of automation and customization in the shape of the sensing loops and the number of sensing loops that is not as easily achievable with current sensor mats. For example, the pattern of sensing loops to be printed may be repeated on multiple substrates, or it may be scaled up or down depending on the size of the substrates and needs of the vehicle manufacture. According to certain implementations, this technology allows custom patterns to be tuned from common stock print patterns, which reduces the time for design and production and increases the reliability of the production of the product.

In certain implementations in which a film base substrate is used, the total thickness of the sensor mat 20, 30, 50 may be between about 60 and about 185 microns. For example, the sensor layer, the dielectric layer for the sensor layer, the shield layer, and the dielectric layer for the shield layer each may be about 10 microns thick and the film substrate may be about 20 microns thick, resulting in a mat having an overall thickness of around 60 microns. In another implementation, the sensor layer and the shield layer each may be about 20 microns thick, the dielectric layers for the sensor and shield layers each may be about 10 microns thick, and the film substrate may be about 125 microns, resulting in a mat having an overall thickness of around 185 microns. In other implementations, a foam or a fabric substrate may be used. In such implementations, the foam substrate may have a thickness of up to about 1.5 mm and the fabric substrate may have a thickness of up to about 1 mm.

In various implementations, the sensor loops may be printed on materials that are already a part of the steering wheel assembly, which can reduce the overall thickness of the steering wheel rim and the materials used in the rim. For example, the sensor loops may be printed on the back of the leather or vinyl skin that makes up the outer layer of the steering wheel rim, for example. Or, the sensor loops may be printed on a surface of an over-molded polymeric foam layer included in the rim, as another example. In other implementations, sensor mats may be produced separately and installed by gluing or otherwise adhering the mats to the inside surface of the outer skin, which may reduce the time for installing the materials in the steering wheel rim and may increase the accuracy of the location of the one or more sensing zones along the steering wheel rim.

In addition, this technology may be applied to manufacturing heater mats for use in steering wheels. For example, FIG. 12 illustrates one implementation of a heater mat 70 manufactured by printing conductive ink onto a base substrate. The heater mat 70 includes one or more heating zones 71 a, 71 b that are each defined by a conductive loop, and supply 73 a, 73 b and return wires 74 a, 74 b extend between each conductive loop 71 a, 71 b, respectively, and power source 75. As shown, the pattern of ink for each of the heating zones 71 a, 71 b is at least in part selected to provide more even heating of the heater mat 70. In particular, a first portion 76 a, 76 b of zones 71 a, 71 b, respectively, are adjacent to where the supply wires 73 a, 73 b connect to the conductive supply trace of each zone, and a second portion 77 a, 77 b of each zone 71 a, 71 b, respectively, are disposed further away from the connection. The thickness of each portion 76 a, 76 b is less than the thickness of each portion 77 a, 77 b to provide greater resistance for the current flowing from each supply wire 73 a, 73 b into each loop 71 a, 71 b, respectively, which forces more of the current toward a distal portion of each conductive loop and provides for more even heating of each zone. The conductive ink is covered by a dielectric layer (not shown).

The power source 75 may be part of the same ECU, such as ECU 40 shown in FIG. 5, in communication with the sensing/shielding mat or it may be part of a separate ECU. In such implementations, the power source 75 can provide heating current to the heater mat 70 until the steering wheel reaches a predetermined temperature or until the power source 75 is otherwise instructed to stop generating current for the heater mat 70.

In addition, according to some implementations, the power source 75 may be the same power source used to generate the voltage signal for the shielding layer. In such an implementation, the power source is configured for selectively generating a voltage signal for the shielding layer and a heating current for the heater layer. The voltage signal may be configured to match, as close as possible, the voltage signal of the sensing loops, and a shielding current may be less than about 200 microamperes. The heating current may be between about 4 and about 8 amperes. For example, the power source may be configured for generating the heating current for one or more conductive loops of the heater layer in response to receiving an “on” signal for the heater. The on signal may be received from a presence signal from the one or more sensing loops indicating presence of a hand adjacent the one or more sensing loops or may be received from a button or other input device in the vehicle. In addition, the power source may be configured for generating the shielding voltage signal for one of the conductive zones of the shielding layer in response to receiving a signal (e.g., an override signal) indicating that sensing in one or more sensing zones, respectively, takes priority over heating. The power source may also configured for ceasing to generate the heating current for the one or more conductive loops of the heater layer in response to a temperature of a respective sensing zone reaching a set temperature. In addition, the power source may be configured for alternately generating the heating current and the shielding voltage signal periodically, such as every about 10 to about 50 milliseconds. In other implementations, the period may be every about 10 to about 100 millieseconds.

Furthermore, in certain implementations (not shown), an additional layer of conductive zones for heating the steering wheel may be printed adjacent the same base substrate as the sensing and shielding layers and is separated from the shielding or sensing layer by a dielectric material.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure. As used in the specification, and in the appended claims, the singular forms “a,” “an,” “the” include plural referents unless the context clearly dictates otherwise. The term “comprising” and variations thereof as used herein is used synonymously with the term “including” and variations thereof and are open, non-limiting terms. While implementations will be described for steering wheel hand detection systems, it will become evident to those skilled in the art that the implementations are not limited thereto.

As utilized herein, the terms “approximately,” “about,” “substantially”, and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numerical ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the invention as recited in the appended claims.

It should be noted that the term “exemplary” as used herein to describe various embodiments is intended to indicate that such embodiments are possible examples, representations, and/or illustrations of possible embodiments (and such term is not intended to connote that such embodiments are necessarily extraordinary or superlative examples).

The terms “coupled,” “connected,” and the like as used herein mean the joining of two members directly or indirectly to one another. Such joining may be stationary (e.g., permanent) or moveable (e.g., removable or releasable). Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate members being attached to one another.

References herein to the positions of elements (e.g., “top,” “bottom,” “above,” “below,” etc.) are merely used to describe the orientation of various elements in the FIGURES. It should be noted that the orientation of various elements may differ according to other exemplary embodiments, and that such variations are intended to be encompassed by the present disclosure.

It is important to note that the construction and arrangement of the sensing system for a steering wheel as shown in the various exemplary embodiments is illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting or layering arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter described herein. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present embodiments.

Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. 

What is claimed is:
 1. A sensor mat configured for being disposed around a steering wheel frame, the sensor mat comprising: a base substrate supporting at least one shielding circuit, at least one sensing circuit, and a plurality of layers of insulating material, wherein the layers of insulating material define a plurality of surfaces in the sensor mat; one or more sensing loops printed with a conductive ink onto one of the plurality of surfaces of the insulating material; one or more shielding loops printed with the conductive ink onto another of the surfaces of insulating material within the sensor mat, wherein the shielding loops and the sensing loops are configured in corresponding pairs of one shielding loop and one sensing loop, wherein the shielding loops overlap at least one area within the plurality of surfaces of the insulating material on which a respective sensing circuit is printed and such that the shielding loops and the sensing loops are separated by at least one of the layers of the insulating material.
 2. The sensor mat of claim 1, wherein the one or more sensing loops are printed onto the base substrate.
 3. The sensor mat of claim 2, wherein the insulating material is a first insulating material, and the sensor mat further comprises: one or more shielding loops printed with the conductive ink onto the first insulating material, and a second insulating material disposed over the one or more shielding loops.
 4. The sensor mat of claim 3, wherein: the one or more sensing loops comprise a first sensing loop and a second sensing loop and the one or more shielding loops comprise a first shielding loop and a second shielding loop, and the first shielding loop is disposed adjacent the first sensing loop and the second shielding loop is disposed adjacent the second sensing loop.
 5. The sensor mat of claim 3, wherein: the one or more sensing loops comprise a first sensing loop and a second sensing loop and the one or more shielding loops comprise a first shielding loop, and the first shielding loop is disposed adjacent the first and second sensing loops.
 6. The sensor mat of claim 3, further comprising one or more shielding feed traces printed with conductive ink onto the first insulating material, each shielding feed trace extending from a corresponding shielding loop toward an edge of the first insulating material.
 7. The sensor mat of claim 2, further comprising one or more sensor return traces printed with conductive ink onto the base substrate and extending from a corresponding sensing loop toward an edge of the base substrate.
 8. The sensor mat of claim 1, wherein the insulating material is a first insulating material, and the sensor mat further comprises one or more shielding loops printed with conductive ink onto a second insulating material disposed on the base substrate, wherein a third insulating material is disposed over the one or more shielding loops and the one or more sensing loops are printed onto the third insulating material.
 9. The sensor mat of claim 1, wherein the conductive ink comprises one or more of the following: silver, carbon, carbon nanotube, graphene, zinc, nickel, tin or copper.
 10. The sensor mat of claim 9, wherein the conductive ink further includes a polymer additive to affect a resistance of the ink.
 11. The sensor mat of claim 9, wherein the conductive ink is capable of withstanding elongation up to about 10%.
 12. The sensor mat of claim 11, wherein the base substrate is capable of elongating at least about 20%.
 13. The sensor mat of claim 11, wherein the conductive ink is printed in a cross hatch or zigzag pattern.
 14. The sensor mat according claim 1, wherein the base substrate comprises a polymer film and a total thickness of the sensor mat is between about 60 microns to about 185 microns.
 15. The sensor mat according to claim 1, wherein the base substrate is an underside of a leather skin configured for being installed around at least a portion of the steering wheel frame rim, and an opposite side of the underside of the leather skin is an outermost layer around the steering wheel frame rim.
 16. The sensor mat of claim 1, wherein the ink is printed adjacent the base substrate in a pattern selected from one or more of the following: cross-hatch, zigzag, grid, spiral, or solid area.
 17. The sensor mat of claim 1, wherein the base substrate comprises one of the following: a polymer foam, a polymer film, leather, vinyl, felt, or non-woven material.
 18. A system for hand sensing in a steering wheel comprising: a sensor mat comprising: a base substrate supporting at least one shielding circuit, at least one sensing circuit, and a plurality of layers of insulating material, wherein the layers of insulating material define a plurality of surfaces in a sensor mat, and wherein the layers are stacked about an axis extending from the base substrate and through the plurality of surfaces; one or more of the sensing circuits printed with conductive ink onto one of the plurality of surfaces of the insulating material; one or more shielding circuits printed with the conductive ink onto another of the surfaces of the insulating material within the sensor mat, wherein the shielding circuits and the sensing circuits are configured in corresponding pairs of one shielding circuit and one sensing circuit, wherein the shielding circuits overlap at least one area within the plurality of surfaces of the insulating material on which a respective sensing surface is printed and such that the shielding circuits and the sensing circuits are separated by at least one of the layers of the insulating material wherein the sensing circuits and the shielding circuits comprise respective return traces extending across the respective one of the plurality of surfaces and another of the surfaces of the insulating material; and an electronic control unit in communication with the sensor mat, the electronic control unit comprising: a processor, and a power source, wherein the processor is configured for receiving a signal from at least one of the one or more sensing loops and determining an indication associated with the signal.
 19. The system of claim 18, wherein the indication is selected from one of the following: a touch, a tap, hold, swipe, or combination thereof.
 20. The system of claim 18, wherein the one or more sensing loops are printed onto the base substrate. 